Stemmed joint implants are used as a treatment for many problems, including osteoarthritis, torn rotator cuffs, severe fractures and pain. However, most implants only have a useful life of approximately ten to fifteen years, at which point, they must be removed and replaced. Sometimes, implants are replaced due to loosening, failure, or infection. The surgical tools currently used for the removal procedure are barbaric and the surgery often results in unintended damage to the surrounding bone and soft tissue from using these tools, which translates to longer time in surgery, a longer recovery time and a higher risk of infection.
Joint replacement, involving insertion of an orthopedic implant or prosthesis, is a common treatment for severe pain caused by osteoarthritis, severe fracture, or a torn rotator cuff. With an aging population, such joint replacement surgeries are increasingly common. In some cases, the original implant must be removed for replacement. Long stemmed implants that are cemented into the bone canal must be broken away from the cement in order to achieve removal. In the case of non-cemented implants, there is often some bone integration with the implant stem's surface, and this fixation must also be broken to remove the implant. If existing methods are not successful, then the patient's bone must be split open to gain access to the implant. This causes increased trauma and risk of complications, as well as prolonging the procedure and additional hospital stay. A reliable atraumatic method for removing the intramedullary stem component of an artificial joint implant is required.
A slaphammer is often used. Although its uses are not restricted to orthopedic surgery, a patent for a surgical slaphammer was filed in 2010 by Donald Huene. (U.S. Pat. No. 8,486,084, which can be found at http://www.google.com/patents/US8486084). A slaphammer is a device that attaches to the extractor/inserter of the implant stem, has a weighted grip and can be used to pull vertically on the implant. The weight is slid up to a hard stop which transfers the momentum of the weight to the implant, and this impact is intended to break the cement fixation and dislodge the implant stem from the bone. Unfortunately, this method is often inadequate to break the cement bond. From here, surgeons have a number of other techniques they can use, each with their own pitfalls.
A commonly used method at the surgeons' disposal is the disimpaction technique. In this technique, osteotomes are inserted along the implant-bone interface with the intention of disrupting the implant's circumferential fixation. This process requires removing bone and cement from around the collar of the prosthesis, exposing the underside and allowing space for a round or square bone tamp. From here, the stem can be malleted out in a retrograde fashion. Flexible (versus rigid) osteotomes can be used when initially disrupting the implant fixation to reduce the number of cortical perforations. Still, this is not a guaranteed method and a wide entry point needs to be created for placement of bone tamps which is difficult to create and not ideal.
Another drawback is that the removal of so much bone can be costly, potentially requiring the need to allograft bone to build up the available bone stock, requiring further healing time. Due to the high impact energies generated during removal (malleting) of the implant stem, there is a high risk of fracturing the bone, which also increases with the patients' age. (Osteotome systems for implant removal are available from companies such as Exactech Inc and Innomed).
The surgeons' next option is to conduct a vertical osteotomy. This method requires a larger incision along the length of the patient's limb, exposing more of the patient's bone. Once more of the bone is exposed, a vertical cut is made lengthwise along the bone extending through the cortical bone to expose the implant stem fixation. Osteotomes are then inserted into the osteotomy and gently twisted in order to “envelope” (or flex) the site creating a visible gap around the underlying implant. The implant can then be malleted out to break any remaining cement bond. Though proven to be generally effective, this method has some severe drawbacks. Greater bone area exposure and added incision length, can result in complications such as infection. Significant hoop stresses are also generated during the “enveloping” stage of the procedure, creating a high risk of fracture of the contralateral cortex, resulting in longer time in surgery, healing period, and additional probability of complications.
One of the most modern methods of implant extraction utilizes ultrasonic stress energy, and is called ultrasonic cement extraction. (For example, U.S. Pat. No. 5,045,054A can be found at http://www.google.com/patents/US5045054, invented by Hood, Klapper and Caillouette of Advanced Osseous Technologies Inc). Ultrasonic cement extraction devices create a dynamic stress wave centered at the tip of the ultrasonic device, that when placed in the PMMA cement surrounding the implant generates enough heat to essentially melt the cement. Once the PMMA mantle is sufficiently heated, the implant stem can be extracted and assorted hooks and chisels may be used to rid the bone canal of any excess cement. However, because of the extreme heat generated by this approach, a great deal of caution must be exercised to prevent significant bone and tissue damage. The ultrasonic waves should be limited to short pulses, while a constant flow of room temperature fluid (saline solution) should be supplied in order to dissipate heat and cool the surrounding areas. These extra considerations introduce an added degree of complexity, and are still not definitive ways of preventing damage to the bone and surrounding tissue.
Another method that is available is the removal of the implant using a pressurized separating fluid. (U.S. Pat. No. 5,290,291 at http://www.google.com/patents/US5290291 filed by Linden of Hall Surgical, a division of Zimmer Inc.). With this technique, a hole must be drilled into the cement mantle connecting the bone to the implant. The end of this drilled hole must have contact with the implant stem so that the nozzle of a fluid pumping device may be inserted. It is imperative that a seal be formed at the nozzle end, so that the pressurized fluid may be pumped in between the prosthetic and cement mantle. Once the critical pressure of cement failure is reached, the cement should deform, fracture and/or separate, thereby releasing the implant. From here, mechanical energy in addition to the fluid pressure may be applied in the form of striking, or pulling, methods such as those used in other techniques. A benefit to this technique is the lack of heat generation. However, the amount of pressure required to force a fluid into the implant stem-cement interface is large and can lead to rupture of the bone before the critical stress point of the cement is reached.
It should be noted at this point, that the impact methods described above involve the application of external impact forces, which are intended to transfer kinetic energy to the implant. To transfer the kinetic energy efficiently requires rigid stabilization of the patient's limb. However, this is not possible and, in practice, the limb is most often simply held steady by an assistant. As the implant and bone are encased in a significant amount of the patient's soft tissues, the assistant cannot provide rigid stabilization of the limb. Thus, much of the impacted energy is absorbed or dissipated into the patient's soft tissues and assistant's arms. Rather than breaking the implant stem's bond, the stem and bone are displaced, causing soft tissue strains which may lead to nerve damage or other complications.
It would be very advantageous to provide an implant extraction tool for removing a cemented or non-cemented implant stem which avoids the above-mentioned limitations.